You all are so great...thanks for all of your suggestions. This is really bad feeling situation and it really helps to hear from you

I will be addressing the situation next week, although still not sure how I will handle it. You all have good suggestions. Keep them coming
As for her being interested in me for more than a friend....Gosh, I hope not!! I am a man only kind of gal

Seriously though, I don't think she is interested like that...she has a very serious boyfriend, but I guess that doesn't mean she is interested in only men. Wow, I hadn't thought of that one...now I really, really don't want her to stay! ha ha
Honestly, I think she is just a more laid back kind of person than me...you know...whatever sounds fun is what she is up for. Not that I don't love fun, but I have boundaries such as this one. Plus, she is a little younger than me, so maybe it is the maturity level??? Maybe she hasn't gotten that college "hang out at whoever's house" thing out of her system??
I do agree though, that it was strange that she assumed an invitation to dinner meant a sleep over. I would never ever assume that with anyone.